1. Field of the Invention
This invention relates to an apparatus for cross-cutting treetrunks, comprising a frame, which is provided with gripping members for engaging a treetrunk from below, with feeding means for imparting a longitudinal movement to the treetrunk, and with a cross-cutting tool, which us operable to move transversely to the longitudinal feeding direction. The devices also comprises a device for measuring lengths.
2. Description of the Prior Art
Such apparatuses are mounted on a suitable vehicle, in most cases suspended from a crane, and are lowered onto the felled tree while the gripping members are open. Thereafter the gripping members engage the treetrunk and support and guide the treetrunk during its further processing. The feeding means move the tree, in most cases past lopping knives, to a cross-cutting device, by means of which the treetrunk is cut into logs having the same length or into logs each having an exactly predetermined length.
In order to permit cross-cutting of the tree into logs having a predetermined length, a measuring device is required, which measures the distance over which the treetrunk has been fed and which causes the treetrunk to be arrested when it has been fed over the predetermined length.
Such an apparatus is known, e.g., from a prospectus of Valmet Logging AB (Prospectus No. 5999 653, May 1989). Lengths are measured by means of a measuring wheel, which is mounted in the frame of the apparatus and is covered in part by a guard for protection.
That arrangement has the disadvantage that the measuring wheel may temporarily disengage the treetrunk if it is curved or uneven, or that the measuring wheel, if it is mounted in a soft spring suspension, will follow any uneven portion of the surface of the surface of the treetrunk. In both cases the accuracy of the measurement will be considerably affected. Besides, the measuring wheel is relatively weak as it is not normally required to transmit forces, and is either exposed, whereby it can easily be damaged or, if it protrudes through an opening from the frame, it may be blocked by wedged bark pieces.
Another apparatus of the kind described hereinbefore is disclosed in a prospectus "Steyr Tree Processor KP 40" of Steyr Forsttechnik Ges.m.b.H. The device for measuring lengths described therein is coupled to the drive means of the feeding means. Whereas that arrangement results in a very robust and reliable structure, some slippage occurs and results in false measurements.